If you go to Cancun there are many excursions you can do. One is to Isla Mujeres, an island with nice beaches 30 minutes away from Cancun, where you can swim, snorkel and scuba dive. You can get to the island by boat from Puerto Juarez, or by joining an organized tour.
In Cancun there are some Mayan Archeological sites you can visit as well. One of them is in the hotel Zone, Ruinas el Rey. A bigger site, El Meco, is just outside the city.
♥ Visit Tagulandang Island ♥